The invention relates generally to medical imaging systems, and more particularly to a composite structure for use in a magnetic resonance imaging system and a method of manufacturing the same.
The vacuum vessel of an MRI magnet is generally made of components that are welded together during assembly of the magnet to form a pressure boundary. Therefore, the function of the vacuum vessel of an MRI magnet is to provide a reliable pressure boundary for maintaining proper vacuum operation. Any leakage or gas permeation over time will increase the vacuum pressure and, consequently, increase the heat load of the magnet.
Vacuum vessels known in the art are usually made of metals such as stainless steel, carbon steel and aluminum. Although, metal vacuum vessels are strong enough to resist vacuum forces, they generate eddy currents and unwanted field distortions in the imaging volume when exposed to an AC field.
Attempts have been made to construct non-metallic vacuum vessels. However, non-metallic vacuum vessels tend to be permeable to gasses and moisture, which hampers the normal vacuum operation.
Similarly, attempts have been made to use thin metallic foils over the non-metallic vacuum composite structures for providing vapor barrier. One major disadvantage with such composite structures is that the metallic foils may not seal properly at the flange joints of the vacuum composite structures.
Thus, there is a need for an impermeable vacuum composite structure that provides reduced field effects from eddy currents.